This invention relates to methods and apparatus for improving the performance of autoperfusion dilatation catheters as used in angioplasty and the like, and more specifically to an arrangement for maintaining a spiral sheath configuration during those procedures.
Dilatation balloon catheters are well known and used regularly for coronary angioplasty procedures and other similar procedures. Atheromatous plaque adhering to a blood vessel wall and restricting blood flow therethrough is compressed against the vessel wall by a balloon that is positioned in the vessel at the plaque location. This dilates the vessel lumen to permit increased blood flow.
A typical balloon catheter includes two lengthwise lumens or channels, one for inflation of an inflatable balloon sealed to the distal catheter end and the other for insertion of a guidewire extending though the catheter to aid in positioning the catheter during use.
Many catheters have been designed for particular uses, having a variety of configurations, methods of construction and methods of use. Most have a generally tubular balloon that, when inflated, temporarily cuts off blood flow through the vessel. Serious consequences can occur when blood flow is stopped for an extended period. Therefore, inflation duration is generally relatively short, typically no more than 150-180 seconds. Longer inflation periods would be very desirable, since better plaque compression could be accomplished. Also, some patients cannot tolerate even short time blood occlusion in some vessels.
Attempts have been made to develop balloon configurations that will permit at least some continued blood flow during plaque compression. For example, catheters having an additional lumen have been used, with openings between the catheter exterior and the added lumen at both ends of the balloon, so that limited blood flow can bypass the balloon occlusion. However, this arrangement has had limited success, since only a very limited amount of blood can flow though the lumen and adding the lumen increases the diameter of the catheter, which itself will tend to retard blood flow. Thus, at most this arrangement will allow a very slightly longer balloon inflation period.
Fogarty et al. in U.S. Pat. No. 4,762,130, Blackshear et al. in U.S. Pat. No. 5,308,356 and others have disclosed catheter balloons with a spiral or corkscrew-like configuration when expanded. Such perfusion balloon catheters are intended to allow blood to flow in a spiral channel path past the balloon during balloon inflation. However, in practice, little if any blood flow is found to occur with these spiral balloons, apparently due to blockage of the balloon channels by the arterial intima or lining and/or expansion of the balloon in the channel region decreasing channel cross sectional area.
Attempts have been made to reinforce the channel of a spiral catheter balloon with a spiral metal or plastic wire engaging the balloon spiral channel, as described by Gurbel et al. in U.S. Pat. No. 5,295,959 and Inderbitzen et al. in U.S. Pat. No. 5,484,411.
These reinforcing wires have been less than fully successful, primarily because expansion of the balloon tends to stress the wire to the point where the channel shape is not retained and the wire is stretched beyond its elastic limits. Further, the wire may be excessively bent while negotiating tortuous paths while the balloon catheter is being emplaced. Where the wire has been stressed to the point where the modulus of elasticity is exceeded the balloon cannot be returned to its original diameter during rewrapping, making the balloon difficult and dangerous to withdraw. In addition, where the wire is simply bonded to the balloon or wrapped around the catheter adjacent to the balloon ends, the bond may be released or the end wraps may unwrap, when the balloon is expanded, resulting in a loose or partially loose wire, which can be very difficult to remove from a body lumen.
Thus, there is a continuing need for improved spiral catheter balloons including a spiral channel retainer that will maintain sufficient perfusion capacity while the balloon is inflated, that will maintain the channel shape during inflation, that will not become permanently deformed during catheter movement through a tortuous lumen path, that will return fully to the uninflated diameter and shape when deflated and that will remain securely attached to the catheter during balloon emplacement, inflation, deflation and withdrawal.